Thermo-poroelastic effects during re-injection in discrete fractures

Our contribution analyses the poroelastic deformation response of a fractured reservoir when water is injected at a lower temperature. During re-injection, because of the cooling effects, the rock surrounding the fractures contracts following the advancement of a thermal front as a function of the advective heat transport properties of the rock. This results in a fracture that gradually opens with time, altering the flow and pressure conditions and the heat transport along the fracture directions. The two-ways couplings of thermal and poroelastic mechanisms imply a strongly non-linear response of the transient fracture permeability. We have studied the problem with an innovative numerical approach that handles fractures as strong discontinuities based on the enhanced discontinuity approach. Multiple fractures are introduced as lower interface elements at the element boundaries and the method solves for continuity, momentum and energy balance in the porous matrix and in the fractures, with heat and mass exchange allow from the two systems. The implementation and analyses are carried out in the finite element software OpenGeoSys-6. We have studied the influence of thermal effects on the pressure, opening and slip evolution of single as well as multiple planar fractures.